Power mechanism and safety lock therefor

ABSTRACT

A lift rack having pivotally collapsable legs is lifted by a hydraulic cylinder. A safety locking device associated with the cylinder includes a bar that moves into successive latching positions with an underlying rack during extension of the cylinder. The locking device may be manually released during the lowering of the rack and is automatically returned to latching capability after being fully retracted.

United States Patent [191 Hansen [451 July 31, 1973 POWER MECHANISM AND SAFETY LOCK THEREFOR [75] Inventor: Warren T. Hansen, Rock Island, Ill.

[73] Assignee: Bear Manufacturing Corp., Rock Island, 111.

22 Filed: Sept. 1,1971

21 Appl. No.: 177,000

[51] Int. Cl. Fl5b 15/26 [58] Field of Search 92/13, 15, 17,18, 92/19, 20, 23; 188/67, 82.3; 254/10 [5 6] References Cited UNITED STATES PATENTS 6/1926 Nilson 92/23 X 8/1929 Gregory... 7/1959 Stixrood 92/19 X 1,000,784 8/1911 Cumming 118/67 X 1,450,366 4/1923 I-Iaseltine... 188/82.3 X

1,590,848 6/1926 Nilson 92/23 X 1,724,926 8/1929 Gregory 92/23 2,706,009 4/1955 Schramm.... 92/19 X 3,251,278 5/1966 Royster 92/18 Primary Examiner-Martin P. Schwadron Assistant Examiner-Abe Hershkovitz Attorney- Lee .1. Gary, Russell W. Pyle et al.-

[57] ABSTRACT A lift rack having pivotally collapsable legs is lifted by a hydrauliccylinder. A safety locking device associated with the cylinder includes a bar that moves into successive latching positions with an underlying rack during extension of the cylinder. The locking device may be manually released during the lowering of the rack and is automatically returned to latching capability after being fully retracted.

-5 Claims, 8 Drawing Figures POWER MECHANISM AND SAFETY LOCK THEREFOR BACKGROUND OF THE INVENTION This invention relates to the combination of a power mechanism and a safety lock therefor and more particularly to a unidirectional catch mechanism operable conjointly with a power mechanism having an extendable part, such as a power cylinder having an extendable piston rod.

Fluid operated cylinders are commonly employed in connection with lifting mechanisms of various types. One type of lifting mechanism is a vehicle lift, such as that which is raised by means of a hydraulic cylinder. Power cylinders of this nature are activated by pressurized fluid urging against a piston. In the event that a pressure loss occurs, the lifting apparatus may suddenly collapse and create a dangerous situation. This is especially true in the case of vehicle racks, where personnel may be working beneath the rack. Thus, it would be desirable to provide a device operable conjointly with a power cylinder to hold the piston rod thereof in extended or partially extended position in case of power or pressure failure, and thereby prevent unexpected collapse of the article being supported.

BRIEF SUMMARY OF THE INVENTION The present invention features a safety lock mechanism that may be mounted externally on a power cylinder having an extendable piston rod and is operable to allow extension of said rod but to substantially prevent return of the rod during extension. For this purpose, a latch arm pivotally connected to the piston rod rides over a series of linearly aligned slots or stops in a rack secured to the cylinder. A manual release may be activated to lift the latch arm out of engagement with the slots to allow the piston rod to retract. The latch arm includes a mechanism that automatically resets the arm in latching position upon full retraction of the rod.

THE DRAWINGS FIG. 1 is a schematic elevational view of a vehicle lift shown in lowered or collapsed position;

FIG. 2 is a view similar to FIG. 1, but showing the lift in extended or elevated position;

FIG. 3 is a fragmentary plan view of a portion of the device shown in FIGS. 1 and 2;

FIGS. 4 through 8 are fragmentary elevational views of a power cylinder and the associated novel locking mechanism shown in successive stages of operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention will be described in connection with a hydraulic vehicle lift, although it will be understood that the principles of the invention are adaptable to any power cylinder having a relatively extendable rod, or generally, to any two parts that are relatively movable away from each other in a generally linear direction.

The vehicle lift is shown schematically in FIGS. 1, 2 and 3 and generally comprises a pair of spaced parallel coextensive runways 10 and 12 having a respective hinged ramp sections 14 and 16 and being connected by cross beams 18, 20 and 21. Drop pans 22 may be provided in the runways 10 and 12 as is well known in the art. The lift is supported on pairs of collapsable legs 24 and 26 which are pivotally connected to respective base supports 28 and 30 at their one end and to the cross beams 18 and 21 at their other end. The pairs of legs 24 and 26 are movable in parallel vertical planes such that the lift may be elevated from a collapsed position and supported in a fully elevated position.

Means, such as ahydraulic cylinder 32 are provided to raise and lower the lift as desired. The hydraulic or other power cylinder 32 is conventional in nature and operation and generally comprises a fluid filled cylinder 34 having a piston sealed therein for reciprocation, said piston being secured to a rod 36. A source of pressurized pneumatic or hydraulic fluid (not shown) is connected to the cylinder 32 for actuation thereof. The cylinder is preferably mounted in a position longitudinally offset from one of the cross beams 20 with the cylinder 34 being pivotally connected to a support 38 secured to an underlying support surface, and the rod 36 being pivotally connected to one of the cross beams, such as the beam 20.

It will be noted in FIGS. 1 and 2 that the leg pairs 24 and 26 are mounted to tilt in the same direction, such that the combination of the stand and the support surface resembles a parallelogram, with the runways l0 and 12 being maintained parallel at all times with the support surface. The power cylinder 32 is mounted in such a manner that the rod 36 is extendable on an angle in the same general direction as the direction of eleva tion of the vehicle rack. Thus, pressurization of the power cylinder 32 causes the rod 36 to extend therefrom and raise the stand to an upright position.

During the lifting of the stand by the power cylinder, a loss of pressure or other malfunction could cause sudden collapse of the lift, thereby resulting in injury to the vehicle supported thereon and to service personnel. .F or this reason, it is desirable to provide a safety device to prevent collapse of the lift while the same is being lifted and while in an extreme elevated position. For this purpose, a rack that is rigidly associated with the cylinder or support surface and having a plurality of spaced stops is engaged by a latch bar or pawl pivotally mounted on the rack or piston rod. The pawl engages and locks against successive stops in the rack in a stepwise manner as the lift is being raised so as to prevent accidental collapse in the event of pressure relaxation or the like. A release mechanism is also associated with the safety device to hold the pawl out of engagement with the rack during intentional lowering of the lift. The pawl release mechanism also includes means to automatically reset the pawl in latching position after the stand has reached full lowered position, thereby assuring operation of the safety device during each lifting operation.

The safety device and release mechanism are shown generally in FIG. 3 and in greater detail in FIGS. 4 through 8. A rack, generally indicated at 40, is secured to the cylinder 34 or is rigidly associated therewith and comprises a straight L-shaped channel member having a base portion 42 secured to the cylinder with an upstanding shoulder defined by a vertical wall 44 spaced from the cylinder and defining an upwardly facing linear guideway hereinafter more fully described. The base has a plurality of linearly aligned and equi-sized notches or slots 46 therein extending coextensivcly with the shoulder 44. Both the shoulder and the spaced slots 46 are disposed substantially parallel to the axis of the cylinder.

A pawl or latch bar 48 is pivotally connected to the cross beam 20 (FIG. 3) and is positioned to overlay the base 42 of the rack 40 between the vertical wall 44 thereof and the cylinder 32. The latch bar 48 includes a downwardly projecting leg 50 at the free end thereof adapted to fit entirely in one of the slots 46 when the bottom surface of the bar is resting on the upper surface of the rack base 42. The leg 50 comprises a sharp or right angle surface 52 on the rearward side thereof or the side facing in the direction of contraction of the piston rod, and a forwardly inclined or cam surface 54 on the other side thereof. The right angle surface 52 is disposed at a 90 or less degree angle to the corresponding abutting slot end so as to prevent motion of the bar 48 in a rearward direction, i.e., a direction substantially parallel to the direction of contraction of the piston rod. Forward movement of the bar 48 relative to the rack 40, however, is possible because the inclined surface 54 causes the leg 50 of the bar to be cammed out of one slot 46 until the next slot is engaged. Thus, with the leg 50 of the bar 48 engaged in one of the slots 46, movement of the bar relative to the rack is substantially limited to one direction, particularly a direction parallel to the direction of extension of the piston rod.

From the foregoing, it will be understood that as the power cylinder 32 is energized to extend the piston rod and raise the lift, the leg 50 of the latch bar 48 travels from one of the slots 46 to the next successive adjacent slot, thereby preventing accidental return of the lift to a lower position. It will also be understood that many possible configurations may be given to the rack 40 or the latch bar 48 to achieve the desired ratchet effect. For example, the rack may comprise upwardly facing and forwardly inclined teeth or other stops, and the leg of the bar may be pointed or otherwise shaped to be engageable step-wise with successive teeth. The pivotally mounted bar rides over successive teeth or stops during extension of the piston and falls into successive locking positions due to its own weight. The slots 46 or their equivalent are sufficient in number to accommodate full extension of the piston rod, and hence the complete raising of the lift, with the last stop preferably being engaged when the lift is in full elevatedposition.

A release mechanism is provided in order to enable lowering of the lift from an upright position and to allow retraction of the piston rod relative to the cylinder. The release mechanism serves to lift the leg of the latch bar 48 out of engagement with the slots 46 in the rack 40 and to maintain the latch bar in such position until the piston rod has been completely retracted. For this purpose, a plate 54, preferably triangular in shape, is pivotally mounted at one apex thereof on the latch bar 48 between the spaced shoulders of a suitable bolt or pivot 56. .The pivot is preferably located. near the free end of the latch bar above the leg 50 thereof, and the plate 54 is mounted on the outer side surface of the latch bar such that it is spaced from said surface and overlaps the vertical wall 44 of the rack 40. A roller 60 is mounted on the rear surface of the plate 54 in a spaced relationship with the pivot 56 and projects toward the cylinder 34 so as to overlie the vertical wall 44 of the rack 40. The roller 60 may thus engage and roll along the linear guideway defined by the upper surface of the wall 44.

Means are also provided to enable manual rotation of the plate 54, said means comprising a pin or bolt 62 pivotally mounted on the plate 54 in a spaced relationship with the bolt 56 and roller 60 and extending outwardly from the plate. The bolt 62 has a transverse aperture in the head thereof receiving one end of a rod or cable 64, the other end of which is slideably mounted in the beam 20 and has a knob 66 (FIGS. 1 and 2) secured thereon to enable remote pulling of the cable 64. The cable 64 is connected to the bolt 62 by suitable means, such as a pair of collars 65 and 67 having set screws therein engaged with the cable on both sides of the transverse aperture.

From the foregoing, it may be seen that the plate 54 acts as a lever pivotally mounted at one end and having a roller mounted between the ends. The plate 54 may pivot between the positions indicated in FIGS. 6 and 7, pivotal movement in a direction toward the end of the rack being limited by a stop 68 secured to the latch bar 48. As the plate 54 is pivoted, the roller 60 engages the wall 44 and acts as a fulcrum, whereby the latch bar 48 is lifted relative to the rack 44, as will be hereinafter more fully explained. As shown in FIGS. 7 and 8, a sharp recess 70 is provided in the vertical wall 44 of the rack above the initial or first slot thereof, i.e., the slot engaged by the latch bar 48 when the piston is fully retracted. Engagement of the roller 60 in the slot causes rotation of the plate 54 to latching position as the piston rod is initally extended.

In operation, the initial configuration of the safety device as shown in FIG. 4, with the leg 50 of the latch bar 48 resting in the first slot, and the roller 60 resting in the recess 70. As the piston rod is extended, the latch bar moves relative to the rack, and the leg 50 is cammed out of the first slot (FIG. 5) and falls into the next adjacent slot (FIG. 6). It may be seen that as second and successive slots are engaged, the roller 60 bears against the vertical wall 44 of the rack, thereby maintaining the plate 54 in a looking or safe position.

In order to retract the piston rod and thereby lower the lift, the knob 66 (FIGS. 1 and 2) is pulled, which causes the plate 54 to rotate toward the knob. In rotating, the plate pivots or is fulcrumed about the roller 60 which is in engagement with the wall 48, thereby moving the pivot 56 and free end of the latch bar upward. The stop 68 is preferably located to engage the plate 54 after it has rotated over center of the roller, such that the plate will not rotate back to a safe position during contraction of the piston rod. It is normally advisable to release the safety device before releasing pressure in the cylinder 32, in order to prevent jamming.

During contraction, the roller 60 rolls along the top of the all 44, thereby maintaining the leg 50 in a raised position spaced from the slots 46. When the piston rod returns to a full retracted position, the roller 60 falls in the recess (FIG. 8). Thereafter, movement of the latch bar toward extended position will cause the plate 54 to rotate about and over center of the roller 60 into a locking or safe position. In this manner, automatic engagement of the safety device is assured with each extension.

It will be understood that various changes or moditications may be made to the preferred embodiment described above without departing from the scope of the appended claims.

Having thus described the invention, what is claimed 1. In combination with a power cylinder having an axial piston rod extendable therefrom, a safety lock device for substantially limiting movement of said rod toward an extended position relative to said cylinder, comprising a rack secured to said cylinder, a series of spaced and aligned slots in said rack, said series being disposed along a line parallel to the axis of said cylinder, latch means pivotally associated with said piston rod and movable therewith, said latch means overlaying said rack and having a leg, opposed surfaces of said leg being engageable with the respective ends of successive slots of said series, a ramp surface on said leg on the side thereof facing the direction of movement of said rod toward extended position, shoulder means on the other side of said leg for locking against a contiguous slot end, a shoulder upstanding from the rack relative to the slots therein, and means for holding said leg out of engagement with said slots comprising a lever pivotally mounted on said latch means adjacent the leg thereof, and roller means on said lever engageable with said shoulder.

2. The combination of claim 1 wherein a recess is provided in the shoulder of said rack near the first of said series of slots, said roller means being engageable with said recess to rotate said lever about said roller means.

3. The combination of claim 1, wherein means are provided for manually rotating said lever about its pivot and turning said latch means about said roller means.

4. In a safety lock mechanism for a power device having a first part extendable from an initial position away from a second part, latch means associated with said first part and stop means associated with said second part, said latch means being operative against said stop means for limiting movement of said first part in a direction away from said second part in a stepwise manner, and release means for disengaging said latch means from said stop means, said release means comprising lever means pivotally mounted on said latch means and operative upon rotation of said lever means in one direction to move said latch means out of engagement with said stop means, a surface associated with said second part, fulcrum means on said lever means for providing a fulcrum against said surface upon rotation of said lever means in said one direction, said fulcrum means being movable along said surface, means for manually rotating said lever means in one direction, and means to catch said lever means in the initial position of said first part and rotate said lever means in the opposite direction.

5. The safety lock mechanism of claim 4 wherein stop means are provided for limiting rotation of said lever means in said one direction to position over center of its pivot. 

1. In combination with a power cylinder having an axial piston rod extendable therefrom, a safety lock device for substantially limiting movement of said rod toward an extended position relative to said cylinder, comprising a rack secured to said cylinder, a series of spaced and aligned slots in said rack, said series being disposed along a line parallel to the axis of said cylinder, latch means pivotally associated with said piston rod and movable therewith, said latch means overlaying said rack and having a leg, opposed surfaces of said leg being engageable with the respective ends of successive slots of said series, a ramp surface on said leg on the side thereof facing the direction of movement of said rod toward extended position, shoulder means on the other side of said leg for locking against a contiguous slot end, a shoulder upstanding from the rack relative to the slots therein, and means for holding said leg out of engagement with said slots comprising a lever pivotally mounted on said latch means adjacent the leg thereof, and roller means on said lever engageable with said shoulder.
 2. The combination of claim 1 wherein a recess is provided in the shoulder of said rack near the First of said series of slots, said roller means being engageable with said recess to rotate said lever about said roller means.
 3. The combination of claim 1, wherein means are provided for manually rotating said lever about its pivot and turning said latch means about said roller means.
 4. In a safety lock mechanism for a power device having a first part extendable from an initial position away from a second part, latch means associated with said first part and stop means associated with said second part, said latch means being operative against said stop means for limiting movement of said first part in a direction away from said second part in a stepwise manner, and release means for disengaging said latch means from said stop means, said release means comprising lever means pivotally mounted on said latch means and operative upon rotation of said lever means in one direction to move said latch means out of engagement with said stop means, a surface associated with said second part, fulcrum means on said lever means for providing a fulcrum against said surface upon rotation of said lever means in said one direction, said fulcrum means being movable along said surface, means for manually rotating said lever means in one direction, and means to catch said lever means in the initial position of said first part and rotate said lever means in the opposite direction.
 5. The safety lock mechanism of claim 4 wherein stop means are provided for limiting rotation of said lever means in said one direction to position over center of its pivot. 